This invention relates to a microwave system which has redundant processing devices and, more particularly, to an approach for accomplishing switching between the processing devices when the primary device fails and the redundant device is activated.
Microwave systems are sometimes used in situations where their operation is critical and cannot be interrupted, or where they are difficult to repair in the event of a failure. For example, microwave amplifier circuits used in communications satellites receive microwave communications signals transmitted from a ground station to the satellite, amplify those signals, and retransmit them back to another ground station. These circuits cannot be permitted to fail, both because their failure would render the entire communications channel useless and because it is difficult to repair the amplifier circuits. Similar considerations apply to microwave communications circuits in deep space and interplanetary missions.
To ensure continuous operation, most microwave systems used in such critical applications are furnished with redundant active components. For example, there may be a primary active amplifier and a backup active amplifier in each communications circuit. The primary active amplifier is used in normal operation, with the backup active amplifier switched off. If the primary active amplifier fails, the backup active amplifier is switched on.
The microwave signal propagating in a waveguide is switched from the primary active amplifier to the backup active amplifier. Available microwave waveguide switches are heavy, costly, complex to integrate into the microwave waveguide system, and consume power. In the case of electro-mechanical or ferrite waveguide switches, the bulkiness of the switch limits the degree of miniaturization that may be achieved. These considerations are particularly troublesome where there are multiple microwave waveguide switches required to interconnect various redundant active devices. Nevertheless, the risk in loss of the communications circuit has been judged to mandate the use of the redundant active components and the associated microwave switches.
There is a need for an improved approach to providing redundancy in microwave circuits that require such redundancy due to their critical nature or inaccessibility for repair. The present invention fulfills this need, and further provides related advantages.
The present invention provides a redundant microwave system wherein switching between a primary microwave processing device and a redundant backup microwave processing device is accomplished without the use of an active switch. The weight, cost, bulk, and possible signal loss of an active switch are saved, but advantages of redundancy are retained. The present approach may be implemented in a wide range of applications.
A redundant microwave system operable to process a microwave signal propagating in a microwave cavity comprises a microwave cavity and a first microwave processing device located exterior to the microwave cavity. The first microwave processing device has a transmissive impedance when the first microwave processing device is operable and a reflective impedance when the first microwave processing device is not operable. A first coupling probe extends from the first microwave processing device to a first probe termination location within an interior of the microwave cavity. A second, redundant, microwave processing device is located exterior to the microwave cavity. The second microwave processing device is substantially identical to the first microwave processing device and has the transmissive impedance when the second microwave processing device is operable and the reflective impedance when the second microwave processing device is not operable. A second coupling probe extends from the second microwave processing device to a second probe termination location within the interior of the microwave cavity. Either of the microwave processing devices may include an impedance-matching network.
The two microwave processing devices may be of any operable type, but are typically amplifiers or receivers. The coupling probes may be of any operable type, but are typically coaxial probes or stripline probes.
There are three particularly preferred embodiments of this approach, In one, the first probe termination location and the second probe termination location are each positioned at about a respective one of the two electric field spatial maxima of a TE(2,0) microwave signal propagating in the waveguide. In a practical implementation, the microwave cavity is a rectangular waveguide having a direction of elongation, a long transverse dimension perpendicular to the direction of elongation, a first sidewall parallel to the direction of elongation and perpendicular to the long transverse dimension, and a second sidewall parallel to the direction of elongation and perpendicular to the long transverse dimension. The first sidewall is spaced apart from the second sidewall by the long transverse dimension, The first probe termination location is about xc2xc of the distance from the first sidewall to the second sidewall, and the second probe termination location is about xc2xe of the distance from the first sidewall to the second sidewall.
In a second embodiment, the first probe termination location and the second probe termination location are each positioned at about the single electric field spatial maximum of a TE(1,0) microwave signal propagating in the waveguide, In a practical implementation, the microwave cavity is a rectangular waveguide having a direction of elongation, a long transverse dimension perpendicular to the direction of elongation, a first sidewall parallel to the direction of elongation and perpendicular to the long transverse dimension, and a second sidewall parallel to the direction of elongation and perpendicular to the long transverse dimension. The first sidewall is spaced apart from the second sidewall by the long transverse dimension. The first probe termination location and the second probe termination location are each about midway between the first sidewall and the second sidewall, positioned closely together and immediately adjacent to each other, but still distinctly two separate probes.
In a third embodiment, the microwave cavity comprises a first volume, a microwave feed in communication with the first volume, and a second volume communicating with the first volume. The second volume is separated into a first region and a second region by a wall. The first probe termination location is within the first region and the second probe termination is within the second region.
In the general approach and all of these specific embodiments, each of the microwave processing devices has two impedance states. When the microwave processing device is active (the xe2x80x9conxe2x80x9d state), its transmissive impedance is such that the microwave signals pass between the microwave cavity and the active microwave processing device, through the coupling probe. That is, the transmissive impedance establishes boundary conditions within the cavity such that there is a mode conversion and propagation of the microwave signal into the coupling probe. When the microwave processing device becomes inactive (the xe2x80x9coffxe2x80x9d state), its reflective impedance is such that the microwave signals do not pass between the microwave cavity and the active microwave processing device, through the coupling probe. That is, the reflective impedance establishes boundary conditions within the cavity such that there is not a mode conversion and propagation of the microwave signal into the coupling probe. Operable values of transmissive and reflective impedances may be readily determined using conventional microwave techniques.
In service, the first microwave processing device is operated as the active primary processing device, and the other, second microwave processing device is inactive as the redundant microwave processing device. If the first microwave processing device fails or is otherwise removed from service, it is switched off so that its impedance results in rejection of the microwave energy. The redundant microwave processing device is switched on, so that it no longer rejects the microwave energy in the microwave cavity and allows it to flow to the second microwave processing device.
The present approach may be contrasted with the usual approach for accomplishing switching in redundant microwave circuits. In the conventional approach, in addition to the two microwave processing devices there is a separate device, an active waveguide switch, that directs microwave energy flowing in the waveguide either to the primary device or to the redundant device. In the present approach, there is a mode conversion between the microwave cavity and the two probes. The load impedances of the microwave processing devices themselves are used to alter the boundary conditions of the waveguide cavity and thence the input impedances of the mode conversions accomplished at the microwave cavity/probe interface, so that no separate active switch is required.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.